So basically you give 1 of your pokemon to an NPC, and it gives you whatever TM's it has. You will obviously lose your pokemon.
Let's say, now that breeding was implemented, your umbreon is kind of useless. You now want to get yourself a wish umbreon, but you also want toxic, a move that your umbreon has but you don't have anything to trade for a new one. Insead of creating an alt. account and get it, you can take your useless umbreon with ivs 0-2 on everything to the Pokemang recycler and throw it into a machine, so you can have your precious TM Toxic again, for your new Umbreon.